finding elements by attribute with lxml

问题:

I need to parse a xml file to extract some data. I only need some elements with certain attributes, here's an example of document:

<root>
    <articles>
        <article type="news">
             <content>some text</content>
        </article>
        <article type="info">
             <content>some text</content>
        </article>
        <article type="news">
             <content>some text</content>
        </article>
    </articles>
</root>

Here I would like to get only the article with the type "news". What's the most efficient and elegant way to do it with lxml?

I tried with the find method but it's not very nice:

from lxml import etree
f = etree.parse("myfile")
root = f.getroot()
articles = root.getchildren()[0]
article_list = articles.findall('article')
for article in article_list:
    if "type" in article.keys():
        if article.attrib['type'] == 'news':
            content = article.find('content')
            content = content.text

回答1:

You can use xpath, e.g. root.xpath("//article[@type='news']")

This xpath expression will return a list of all <article/> elements with "type" attributes with value "news". You can then iterate over it to do what you want, or pass it wherever.

To get just the text content, you can extend the xpath like so:

root = etree.fromstring("""
<root>
    <articles>
        <article type="news">
             <content>some text</content>
        </article>
        <article type="info">
             <content>some text</content>
        </article>
        <article type="news">
             <content>some text</content>
        </article>
    </articles>
</root>
""")

print root.xpath("//article[@type='news']/content/text()")

and this will output ['some text', 'some text']. Or if you just wanted the content elements, it would be "//article[@type='news']/content" -- and so on.

回答2:

Just for reference, you can achieve the same result with findall:

root = etree.fromstring("""
<root>
    <articles>
        <article type="news">
             <content>some text</content>
        </article>
        <article type="info">
             <content>some text</content>
        </article>
        <article type="news">
             <content>some text</content>
        </article>
    </articles>
</root>
""")

articles = root.find("articles")
article_list = articles.findall("article[@type='news']/content")
for a in article_list:
    print a.text